Seismogenic sources potentially responsible for earthquakes with<i>M</i>≥ 6 in the eastern Southern Alps (Thiene-Udine sector, NE Italy)

Abstract

New geomorphological and structural data permitted to define the active faulting framework of\nthe eastern Southern Alps (NE Italy). All the active faults detected in the investigated area are\nthrust segments of the complex thrust system,which has been responsible for the latest building\nof the Eastern Southalpine chain (ESC). Geomorphological investigations were performed to\nidentify the surficial traces of recent fault activity, generally represented by gentle scarps\nconnecting uplifted palaeolandscapes of Quaternary age with the flat and lower areas of the\nVenetian and Friulian plains. Surficial and subsurficial data (the latter from reflection seismic\nprofiles) available for the investigated faults indicate that the thrusts have been responsible\nfor the displacement of the entire wedge of Quaternary deposits. In the western sector of\nthe investigated area, the six recognized fault segments represent portions of a 100-km-long\nthrust system, at the boundary between the Alpine relief and the plain areas. In the eastern\nsector, active tectonics is the result of parallel thrust segments, located both in the Alpine\nmountainous area and in the Friulian plain. The 3-D geometry of the active thrust segments has\nbeen derived from new structural surficial surveys and the interpretation of reflection seismic\nprofiles for a total length of 1700 km. On this basis, we defined the geometry of 10 seismogenic\nsources whose dimensions are consistent with the occurrence of earthquakes with M ≥ 6. The\ncomparison between the source geometry and the highest intensity data point distribution of\nlarge historical earthquakes has permitted to make hypotheses on the association of past seismic\nevents to specific seismogenic sources. This procedure indicated that no large historical events\ncan be attributed to three sources (Montello-Conegliano, Arba-Ragogna, Medea). This may\nindicate an elapsed time since the last activation of more than eight centuries, based on the\ncompleteness of the historical catalogues. The available data define, therefore, sources (and\nrelated areas) for which a high level of seismic hazard may be invoked.